I tried to reintroduce Linux


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Dedicated hardware used by users to input and output to a computer However, currently, a terminal emulator is used, which is a physical terminal implemented by ** software **.

Various ways of being called



Shell troubleshooting

Ctr + key is represented by ** ^ key ** on the shell

Command history

Ctr + r


Mode to search history every time you enter a character further



find ./ -type f -name aaa.txt -print


Shell variables

Variables used inside bash. Since it is referenced by bash, there are many shell variables with special meanings that can be customized.

echo $val1

Environment variable

** Environment variables can be referenced by external commands ** ** Many shell variables are set as environment variables **

export shell variable name

bash config file

Login shell loading order


Non-login shell loading order


Use properly

** Many settings need to be set every time you start bash, so you can write them in .bashr **

Users, groups and permissions

File permissions

-rw-r--r--.  1 root root      21554 Nov 15  2018 test

Owner: Group: Other users

Directory permissions

drwxr-xr-x   2 root root       4096 Mar 14 17:00 test-test

Directory permissions determine whether files can be deleted If x is set in the directory, cd can move to that directory and read / write files under the directory.

Root user


su - //Initialized to the root user environment
su   //Only the user switches while maintaining the current environment such as environment variables and the current directory.

sudo Used to execute commands as another user

sudo cat /etc/shadow

Currently asked for user password You can execute commands if you are allowed

Allow sudo to user

/etc/sudoers Edit with visudo command

All commands can be executed by belonging to the wheel group

<User or%group> <Machine name>=(<Authority>)<command>
%wheel ALL=(ALL) ALL

Minimize operations as root user with sudo


View ps command process

TTY means terminal. UNIX option to add hyphen The BSD option does not have a hyphen. The BSD option seems to be the mainstream.

Process running in the current terminal

# ps
  PID TTY          TIME CMD
24021 pts/0    00:00:00 su
24022 pts/0    00:00:00 bash
26512 pts/0    00:00:00 ps

Process running by ** current user ** f also indicates parent and child

# ps xf

View all processes running on your system

# ps ax

The one I use often

# ps auxfwww  //Details with x Do not limit display width with www

UNIX option (with hyphen)

# ps -ef  //e to show all processes f f to parent and child

kill command

Command to send a signal

kill-signal name

The default is TERM

kill -TERM process ID

TERM is finished. Depending on the type of program, the current state is saved or the temporary file is deleted when the TERM signal is received, so it is better to kill it first and then forcibly terminate it.


Standard error output is a channel for outputting program error messages.

Standard error output redirect

ls aaaaa 2> aaa.txt

Combine standard output (1) and standard error output (2) 2 to 1

ls aaaa > aaaa.txt 2>&1

Standard output to aaaa.txt. Standard error output to the same as 1. & 1 represents standard output


Hide error messages

ls / /xxxxx 2> /dev/null

grep Enclose the regular expression in ``. grep 't[ef]'

If you want to use a regular expression, specify grep -E that can use extended regular expressions.

Extended regular expression

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